Upgrade old irrigation systems first, say scientists

Last modified
August 07, 2012 13:23

Farmers are responding to the growing problem of water scarcity by upgrading their irrigation systems. But a study in Environmental Research Letters (ERL) shows that while new irrigation systems save water, the only sure way to also save energy is to prioritize the replacement of the oldest, most inefficient systems. Although the study focused on Australian agriculture, its authors say the results should apply elsewhere too.

According to United Nations estimates, by 2025 roughly 1.8 billion
people will be living in regions of absolute water scarcity, while
two-thirds of the world's population will be living in water-stressed
conditions. In Australia, the government considers the problem to lie in
part with old irrigation systems. These include furrow irrigation, in
which water is syphoned from nearby distribution channels, and
hand-shift sprinklers, in which water is pumped through aluminium piping
with sprinklers attached.

Newer irrigation systems, on the other hand, use increased pressure to
deliver water more efficiently: they include pressurized sprinkler
systems, which move mechanically over a crop, and trickle systems, which
sit under the earth and deliver water straight to crop roots.

In the hope of tackling increasing water scarcity, the Australian
government is encouraging the adoption of these newer irrigation
systems. But there's a trade-off; the newer systems are likely to need
increased use of diesel and electricity to power water pumps, which
means increased greenhouse-gas emissions.

Kate Reardon-Smith and colleagues at the University of Southern
Queensland decided to find out how big this trade-off is by assessing
five different Australian farms that were upgrading their irrigation
systems. To do this, they collected information about the running of the
farms in order to calculate the expected water usage, the
carbon-dioxide equivalent greenhouse emissions and the financial return.

All the newer irrigation systems used less water. However, the
researchers found that it was only by replacing the oldest irrigation
systems, such as hand-shift sprinklers, that farmers could also save
energy. This is a "win-win" upgrade, they explain. "[Our] results
suggest that priority should be given, in implementing on-farm
infrastructure investment priority, to replacing inefficient and
energy-intensive sprinkler systems," said Reardon-Smith. "Our
conclusions regarding tradeoffs are applicable globally."

Despite this clear recommendation, however, the details of the results
are more mixed. Although irrigation-related energy emissions went down
only for the upgrading of very old systems, the total emissions also
went down for the upgrading of some newer systems. Reardon-Smith and
colleagues believe that this is because the newest systems allow farmers
to perform so-called precision agriculture – such as distributing
fertilizer, which has a high carbon footprint, through the irrigation
system. So does this mean that there is no drawback to upgrading
irrigation systems after all?

Reardon-Smith warns not to be too hasty in drawing that conclusion. "It
is important to acknowledge though that our case-study approach
essentially raises this as a hypothesis, and that this should be tested
through more comprehensive analysis," she said.